Bartels Mette Damkjær, Knudsen Danah, Westh Henrik, Schønning Kristian
Department of Clinical Microbiology, Copenhagen University Hospital - Amager and Hvidovre, Copenhagen, Denmark.
Department of Clinical Medicine, University of Copenhagen, Copenhagen, Denmark.
Eur J Clin Microbiol Infect Dis. 2021 Oct;40(10):2177-2183. doi: 10.1007/s10096-021-04272-9. Epub 2021 May 11.
Enrichment culture (EC) remains gold standard for detecting MRSA colonisation, but molecular methods shorten turnaround time. The CE-marked automated Hologic Panther Fusion MRSA Assay (HPFM) is validated for nasal swabs. We compared HPFM with EC following an in-house PCR for detection of MRSA in nasal, pharyngeal, and perineal ESwabs. The same ESwabs were analysed using HPFM and inoculated in selective Tryptic Soy Broth (TSB) for overnight incubation. TSBs were screened by a PCR targeting nuc, femA, mecA, and mecC. Only samples with PCR results compatible with MRSA presence were inoculated onto 5% blood agar and chromogenic MRSA plates. HPFM detected MRSA in 103 of 132 EC positive samples indicating a sensitivity of 78.0% across sample types. When paired TSBs of 29 EC positive/HPFM negative samples were re-analysed by HPFM, MRSA was detected in 17/29 TSBs indicating that enrichment will increase the sensitivity of HPFM. HPFM analyses of cultured isolates from the remaining 12 EC positive/HPFM negative samples failed to detect orfX. HPFM reported the presence of MRSA in 22 samples where EC failed to identify MRSA. Fifteen of these ESwabs had been kept and direct culture without enrichment identified MRSA in seven samples. HPFM was useful for all sample sites. Compared to EC, the sensitivity of HPFM was limited because of lack of analytical sensitivity and failure to detect all MRSA variants. Failure of some MRSA-containing samples to enrich in cefoxitin-containing TSB indicates an unappreciated limitation of EC, which may lead to underestimation of the specificity of molecular assays.
富集培养(EC)仍然是检测耐甲氧西林金黄色葡萄球菌(MRSA)定植的金标准,但分子方法可缩短周转时间。具有CE标志的自动化Hologic Panther Fusion MRSA检测法(HPFM)已通过鼻拭子验证。我们在对鼻、咽和会阴ESwab样本进行内部聚合酶链反应(PCR)检测MRSA后,将HPFM与EC进行了比较。使用HPFM对相同的ESwab样本进行分析,并接种到选择性胰蛋白胨大豆肉汤(TSB)中过夜培养。通过针对nuc、femA、mecA和mecC的PCR对TSB进行筛查。仅将PCR结果与MRSA存在相符的样本接种到5%血琼脂和显色MRSA平板上。HPFM在132个EC阳性样本中的103个中检测到MRSA,表明跨样本类型的灵敏度为78.0%。当对29个EC阳性/HPFM阴性样本的配对TSB重新进行HPFM分析时,在17/29个TSB中检测到MRSA,这表明富集可提高HPFM的灵敏度。对其余12个EC阳性/HPFM阴性样本的培养分离株进行HPFM分析未能检测到orfX。HPFM报告在22个样本中存在MRSA,而EC未能识别出MRSA。其中15个ESwab样本被保存,未经富集的直接培养在7个样本中鉴定出MRSA。HPFM对所有样本部位均有用。与EC相比,由于缺乏分析灵敏度且未能检测到所有MRSA变体,HPFM的灵敏度有限。一些含MRSA的样本未能在含头孢西丁的TSB中富集表明EC存在未被认识到的局限性,这可能导致对分子检测特异性的低估。